reed@android.com | 8a1c16f | 2008-12-17 15:59:43 +0000 | [diff] [blame^] | 1 | #include "SkFloatBits.h" |
| 2 | #include "SkMath.h" |
| 3 | |
| 4 | /****************************************************************************** |
| 5 | SkFloatBits_toInt[Floor, Round, Ceil] are identical except for what they |
| 6 | do right before they return ... >> exp; |
| 7 | Floor - adds nothing |
| 8 | Round - adds 1 << (exp - 1) |
| 9 | Ceil - adds (1 << exp) - 1 |
| 10 | |
| 11 | Floor and Cast are very similar, but Cast applies its sign after all other |
| 12 | computations on value. Also, Cast does not need to check for negative zero, |
| 13 | as that value (0x80000000) "does the right thing" for Ceil. Note that it |
| 14 | doesn't for Floor/Round/Ceil, hence the explicit check. |
| 15 | ******************************************************************************/ |
| 16 | |
| 17 | #define EXP_BIAS (127+23) |
| 18 | #define MATISSA_MAGIC_BIG (1 << 23) |
| 19 | |
| 20 | static inline int unpack_exp(uint32_t packed) { |
| 21 | return (packed << 1 >> 24); |
| 22 | } |
| 23 | |
| 24 | #if 0 |
| 25 | // the ARM compiler generates an extra BIC, so I use the dirty version instead |
| 26 | static inline int unpack_matissa(uint32_t packed) { |
| 27 | // we could mask with 0x7FFFFF, but that is harder for ARM to encode |
| 28 | return (packed & ~0xFF000000) | MATISSA_MAGIC_BIG; |
| 29 | } |
| 30 | #endif |
| 31 | |
| 32 | // returns the low 24-bits, so we need to OR in the magic_bit afterwards |
| 33 | static inline int unpack_matissa_dirty(uint32_t packed) { |
| 34 | return packed & ~0xFF000000; |
| 35 | } |
| 36 | |
| 37 | // same as (int)float |
| 38 | int32_t SkFloatBits_toIntCast(int32_t packed) { |
| 39 | int exp = unpack_exp(packed) - EXP_BIAS; |
| 40 | int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG; |
| 41 | |
| 42 | if (exp >= 0) { |
| 43 | if (exp > 7) { // overflow |
| 44 | value = SK_MaxS32; |
| 45 | } else { |
| 46 | value <<= exp; |
| 47 | } |
| 48 | } else { |
| 49 | exp = -exp; |
| 50 | if (exp > 25) { // underflow |
| 51 | exp = 25; |
| 52 | } |
| 53 | value >>= exp; |
| 54 | } |
| 55 | return SkApplySign(value, SkExtractSign(packed)); |
| 56 | } |
| 57 | |
| 58 | // same as (int)floor(float) |
| 59 | int32_t SkFloatBits_toIntFloor(int32_t packed) { |
| 60 | // curse you negative 0 |
| 61 | if ((packed << 1) == 0) { |
| 62 | return 0; |
| 63 | } |
| 64 | |
| 65 | int exp = unpack_exp(packed) - EXP_BIAS; |
| 66 | int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG; |
| 67 | |
| 68 | if (exp >= 0) { |
| 69 | if (exp > 7) { // overflow |
| 70 | value = SK_MaxS32; |
| 71 | } else { |
| 72 | value <<= exp; |
| 73 | } |
| 74 | // apply the sign after we check for overflow |
| 75 | return SkApplySign(value, SkExtractSign(packed)); |
| 76 | } else { |
| 77 | // apply the sign before we right-shift |
| 78 | value = SkApplySign(value, SkExtractSign(packed)); |
| 79 | exp = -exp; |
| 80 | if (exp > 25) { // underflow |
| 81 | exp = 25; |
| 82 | } |
| 83 | // int add = 0; |
| 84 | return value >> exp; |
| 85 | } |
| 86 | } |
| 87 | |
| 88 | // same as (int)floor(float + 0.5) |
| 89 | int32_t SkFloatBits_toIntRound(int32_t packed) { |
| 90 | // curse you negative 0 |
| 91 | if ((packed << 1) == 0) { |
| 92 | return 0; |
| 93 | } |
| 94 | |
| 95 | int exp = unpack_exp(packed) - EXP_BIAS; |
| 96 | int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG; |
| 97 | |
| 98 | if (exp >= 0) { |
| 99 | if (exp > 7) { // overflow |
| 100 | value = SK_MaxS32; |
| 101 | } else { |
| 102 | value <<= exp; |
| 103 | } |
| 104 | // apply the sign after we check for overflow |
| 105 | return SkApplySign(value, SkExtractSign(packed)); |
| 106 | } else { |
| 107 | // apply the sign before we right-shift |
| 108 | value = SkApplySign(value, SkExtractSign(packed)); |
| 109 | exp = -exp; |
| 110 | if (exp > 25) { // underflow |
| 111 | exp = 25; |
| 112 | } |
| 113 | int add = 1 << (exp - 1); |
| 114 | return (value + add) >> exp; |
| 115 | } |
| 116 | } |
| 117 | |
| 118 | // same as (int)ceil(float) |
| 119 | int32_t SkFloatBits_toIntCeil(int32_t packed) { |
| 120 | // curse you negative 0 |
| 121 | if ((packed << 1) == 0) { |
| 122 | return 0; |
| 123 | } |
| 124 | |
| 125 | int exp = unpack_exp(packed) - EXP_BIAS; |
| 126 | int value = unpack_matissa_dirty(packed) | MATISSA_MAGIC_BIG; |
| 127 | |
| 128 | if (exp >= 0) { |
| 129 | if (exp > 7) { // overflow |
| 130 | value = SK_MaxS32; |
| 131 | } else { |
| 132 | value <<= exp; |
| 133 | } |
| 134 | // apply the sign after we check for overflow |
| 135 | return SkApplySign(value, SkExtractSign(packed)); |
| 136 | } else { |
| 137 | // apply the sign before we right-shift |
| 138 | value = SkApplySign(value, SkExtractSign(packed)); |
| 139 | exp = -exp; |
| 140 | if (exp > 25) { // underflow |
| 141 | exp = 25; |
| 142 | } |
| 143 | int add = (1 << exp) - 1; |
| 144 | return (value + add) >> exp; |
| 145 | } |
| 146 | } |
| 147 | |
| 148 | float SkFloatBits_intToFloatNative(int x); |
| 149 | float SkFloatBits_intToFloatNative(int x) { |
| 150 | return x; |
| 151 | } |
| 152 | |
| 153 | float SkIntToFloatCast(int32_t value) { |
| 154 | if (0 == value) { |
| 155 | return 0; |
| 156 | } |
| 157 | |
| 158 | int shift = EXP_BIAS; |
| 159 | |
| 160 | // record the sign and make value positive |
| 161 | int sign = SkExtractSign(value); |
| 162 | value = SkApplySign(value, sign); |
| 163 | |
| 164 | if (value >> 24) { // value is too big (has more than 24 bits set) |
| 165 | int bias = 8 - SkCLZ(value); |
| 166 | SkDebugf("value = %d, bias = %d\n", value, bias); |
| 167 | SkASSERT(bias > 0 && bias < 8); |
| 168 | value >>= bias; // need to round? |
| 169 | shift += bias; |
| 170 | } else { |
| 171 | int zeros = SkCLZ(value << 8); |
| 172 | SkASSERT(zeros >= 0 && zeros <= 23); |
| 173 | value <<= zeros; |
| 174 | shift -= zeros; |
| 175 | } |
| 176 | |
| 177 | // now value is left-aligned to 24 bits |
| 178 | SkASSERT((value >> 23) == 1); |
| 179 | SkASSERT(shift >= 0 && shift <= 255); |
| 180 | |
| 181 | SkFloatIntUnion data; |
| 182 | data.fSignBitInt = (sign << 31) | (shift << 23) | (value & ~MATISSA_MAGIC_BIG); |
| 183 | return data.fFloat; |
| 184 | } |
| 185 | |
| 186 | float SkIntToFloatCast_NoOverflowCheck(int32_t value) { |
| 187 | if (0 == value) { |
| 188 | return 0; |
| 189 | } |
| 190 | |
| 191 | int shift = EXP_BIAS; |
| 192 | |
| 193 | // record the sign and make value positive |
| 194 | int sign = SkExtractSign(value); |
| 195 | value = SkApplySign(value, sign); |
| 196 | |
| 197 | int zeros = SkCLZ(value << 8); |
| 198 | value <<= zeros; |
| 199 | shift -= zeros; |
| 200 | |
| 201 | SkFloatIntUnion data; |
| 202 | data.fSignBitInt = (sign << 31) | (shift << 23) | (value & ~MATISSA_MAGIC_BIG); |
| 203 | return data.fFloat; |
| 204 | } |
| 205 | |